1. Field of the Invention
The present invention relates to a method of edge bevel rinse, and more particularly, to a method that optically projects a reference pattern on a wafer for accurately controlling the position of medicament injection, and therefore can remove a coating material layer positioned in a bevel region of the wafer.
2. Description of the Prior Art
The photolithography process plays a very important role in semiconductor and micro electro-mechanic system (MEMS) manufacturing. Normally, the number of photolithography processes somehow reflects the complexity of semiconductor devices or MEMS devices, and therefore the yield of the photolithography process is crucial to the quality of the devices.
A photolithography process generally includes three steps, which are photoresist coating, exposure, and development. Since photoresist coating is the initial step, it directly affects the yield of successive processes. For the photoresist coating process, the photoresist layer coated on a wafer must have a uniform thickness, and normally this step is carried out by spin coating technique. In a spin coating process, the wafer is mounted on a spindle of a spin coating apparatus, and the photoresist layer is applied to the wafer when the wafer is spinning. By virtue of centrifugal force, the photoresist layer is supposed to be uniformly distributed on the surface of the wafer. Practically, the photoresist layer positioned in a central region of the wafer has a uniform thickness, however, the photoresist layer positioned in a bevel region tends to pile up. This phenomenon is known as edge bead. The photoresist piling up in the bevel region is unfavorable to successive processes, and may cause contamination inside the apparatus. As a result, an edge bevel rinse process is generally required to remove the photoresist layer positioned in the bevel region.
Please refer to FIG. 1. FIG. 1 is a schematic diagram illustrating a conventional method of edge bevel rinse using a semi-automatic coating apparatus. As shown in FIG. 1, a wafer 10 is mounted on a platform 22 of a semi-automatic coating apparatus 20. The platform 22 is structurally connected to a spindle 24, so that the wafer 10 can spin at a certain rate when processed. When a spin coating process is carried out, a photoresist layer 12 will be formed on the surface of the wafer 10. As previously described, the wafer 10 includes a central region and a bevel region, and photoresist tends to pile up in the bevel region. Therefore, chemical medicament has to be injected in the bevel region to resolve the photoresist layer 12, so as to draw off the photoresist layer 12 positioned in the bevel region by centrifugal force. The operator who operates an injector 26, nevertheless, has a problem in accurately injecting the chemical medicament in the bevel region because there is no viewable interface between the central region and the bevel region. In such a case, the yield of the edge bevel rinse process is frequently degraded for many reasons e.g. an inexperienced operator or a visional bias.